The Global Positioning System (GPS) is a worldwide satellite navigational system formed by approximately 24 satellites orbiting the earth and their corresponding receivers on the earth. The satellites orbit the earth at approximately 12,000 miles above the surface and make two complete orbits every 24 hours. The GPS satellites continuously transmit digital radio signals that contain data on the satellites location and the exact time to the earth-bound receivers. Based on this information the receivers know how long it takes for the signal to reach the receiver on earth. Various uses for GPS receivers have emerged over the years, from location tracking for drivers and hikers to flight tracking for aircraft. More recently, the U.S. military has implemented the use of GPS receivers, together with transmitters, on vehicles and soldiers on foot. These devices are used to log and communicate the position data of each GPS device to a central command which combines all such position data and creates a complete picture of all units and their locations.
One of the U.S. military's uses for such a communications network for exchanging position data is for realistic training exercises. For example, Multiple Integrated Laser Engagement System (MILES) is a military training system that provides a realistic battlefield environment for soldiers involved in training exercises. MILES provides tactical engagement simulation for direct fire force-on-force training using eye safe laser “bullets.” Each individual and vehicle in the training exercise has a detection system to sense hits and perform casualty assessment. Laser transmitters are attached to each individual and vehicle weapon system and accurately replicate actual ranges and lethality of the specific weapon systems. MILES training has been proven to dramatically increase the combat readiness and fighting effectiveness of military forces.
Soldiers use MILES devices primarily during force-on-force exercises, from squad through brigade level, to simulate the firing and effects of actual weapons systems. These weapons systems include the M1 Abrams Tank, Bradley Infantry Fighting Vehicle, M113 Armored Personnel Carrier, wheeled vehicles and other non-shooting targets. Additionally, basic MILES simulations address anti-armor weapons, machine guns, rifles, and other ancillary items, such as a controller gun, within the program. Combat vehicles, support vehicles and individual solders are instrumented with a GPS receiver for position location determination and a transmitter for sending all recorded data back to central command. All player activity is recorded during an exercise. Position location, and direct and indirect fire event reporting is accomplished through the associated transmitter.
One of the restrictions on the mobile units used on individual soldiers and some vehicles is energy expenditure. These mobile GPS units run on battery power, which is finite and sometimes too short. As such, various aspects of the system often drain battery power rather quickly. One example is the periodic nature by which a GPS device determines position data, even if it has not moved since the last position determination. This can be redundant and wasteful of battery power. Another example of wastefulness of battery power is the periodic nature by which a GPS device transmits position data, even if it has not moved since the last transmission. This can also be redundant and wasteful. GPS devices also transmit position data periodically, even if direction and speed has not changed since the last transmission. This is not an optimal use of resources.
Another problem with the mobile units used during training exercises is radio attenuation and radio frequency (RF) reflections. Various environmental factors can affect the strength, path and overall structure of a radio signal. Varied terrain such as mountains, forests and hills can reduce signal strength and sometimes block the signal completely. Likewise, man-made structures such as building and vehicles can attenuate a radio signal and garble the information within it. Further, human bodies themselves can attenuate radio signals, which is a particular problem with GPS units and transmitters that are mounted on a foot soldier. One approach to the problem of human body attenuation is mounting the transmitter antenna on the head or helmet of the wearer. Although this works in some instances, mounting an antenna on a wearer's head can be unwieldy and uncomfortable for the individual. Further, although placement of the antenna in this location may promote reception and transmission when the wearer is standing up, this does not hold true when the individual is lying on the ground or in a prone position. Thus, in these positions the placement of the antenna on the wearer's head is not beneficial.
Therefore, a need exists to overcome the problems with the prior art as discussed above, and particularly for a more efficient way for logging and communicating position data.